The EGF growth factor (Epidermal Growth Factor) is a polypeptide synthesised in numerous organs and whose stimulatory action on cell proliferation has been demonstrated on glial cells, mesenchymatous cells and epithelial cells in culture. In the respiratory epithelium, St George et al. (Am. J. Respir. Cell Mol. Biol., 1991, 4, 95-101) have shown that EGF is involved in the foetal development of the tracheobronchial secretory system of monkeys. Stahlman et al. (Lab. Invest., 1989, 60, 539-547) have demonstrated, by immunochemistry, the presence of EGF in respiratory tissue during foetal development in man. On the other hand, it has been shown in animals that EGF has no effect on the proliferation of epithelial cells of dog trachea in culture but that it promotes the response of these same cells to stimulation by beta-adrenergics (Van Scott, Am. J. Physiol., 1988, 255, C237-C245). In contrast, Wu et al. (Am. Rev. Respir. Dis., 1985, 132, 311-320) have reported that the omission of EGF from the culture medium induces a decrease in the proliferation of human nasal epithelial cells.